The present invention is directed to a head suspension with a rigid region having a railed region and a non-railed region. A stiffener that extends along at least part of the non-railed region and 50% or less of the length of the railed region closest to the spring region is attached to the rigid region.
Information storage devices typically include a head for reading and/or writing data onto the storage medium, such as a disk within a rigid disk drive. An actuator mechanism is used for positioning the head at specific locations or tracks in accordance with the disk drive usage. Linear and rotary actuators are known based on the manner of movement of the head. Head suspensions are provided between the actuator and the head and support the head in proper orientation relative to the disk surface.
In a rigid disk drive, head suspensions are provided which support a read/write head to xe2x80x9cflyxe2x80x9d over the surface of the rigid disk when it is spinning. Specifically, the head is typically located on a slider having an aerodynamic design so that the slider flies on an air bearing generated by the spinning disk. In order to establish the fly height, the head suspension is also provided with a spring force counteracting the aerodynamic lift force.
A head suspension of the type used in a rigid disk drive comprises a load beam and a flexure to which the slider is to be mounted. Load beams normally have an actuator mounting portion, a rigid section, and a spring region between the actuator mounting region and the rigid section that provides the aforementioned spring force. The flexure is provided at the distal end of the load beam to which the slider is mounted and permits pitch and roll movements of the slider to follow disk surface fluctuations. Flexures are known that are integrated into the design of the load beam and those formed as a separate element fixed to the rigid region of the load beam.
In providing the spring force to the rigid section of the load beam for counteracting the aerodynamic lift force against a slider, a preformed bend or radius is made in the spring region of the load beam. The radius provides the spring force and thus a desired gram loading to the slider for a predetermined offset height, the offset height being a measurement of the distance between the mounting height of the head suspension and the slider at xe2x80x9cflyxe2x80x9d height. Constraints of the drive design, including the spacing of the disks within the drive, factor into the predetermined offset height. In any case, the gram load at the offset height provides the counteracting force to the aerodynamic lift force to establish the xe2x80x9cflyxe2x80x9d height of the slider above a disk surface. As used hereinafter, the term xe2x80x9cloadedxe2x80x9d refers to a head suspension and slider at xe2x80x9cflyxe2x80x9d height and in equilibrium under the influence of the aerodynamic lift force and the oppositely acting spring force of the head suspension.
The radius area of the spring region is not only responsible for loading, but has also been determined to have a large impact on torsional resonance characteristics of the head suspension. Resonance frequencies of the head suspension, if not controlled, can lead to off-track error within such a disk drive. Head suspensions are designed to optimize performance even at resonance frequencies, which include a lateral bending mode and torsional modes. More particularly, it is a design criterion to increase certain resonance frequencies to be higher than the vibrations experienced in the disk drive application. Additionally, it is desirable to reduce or eliminate the movement or gain of the head at the resonance frequencies of the head suspension.
Torsional and lateral bending modes are beam modes that are dependent on cross-sectional properties along the length of the load beam. These modes also result in lateral movement of the slider at the end of the head suspension assembly. Torsional modes sometimes produce a mode shape in which the tip of the resonating head suspension assembly moves in a circular fashion. However, since the slider is maintained at an offset height by the stiffness of the applied spring force, only lateral motion of the rotation is seen at the slider. The lateral bending mode (often referred to as xe2x80x9cswayxe2x80x9d) is primarily lateral motion.
The lateral bending mode is normally controlled by the design of the cross-section of the load beam, i.e., side rails, channels, and the like. It is typically desirable to control the resonance frequency of the lateral bending mode so that it is higher than the frequencies that are experienced in the disk drives within which they are to be used.
For example, U.S. Pat. No. 5,006,946 (Matsuzaki) discloses a head suspension with side rails and a longitudinal plate of polymeric resinous material. The polymeric material extends from the mounting region, across the spring region and along at least a portion of the rigid region. U.S. Pat. No. 5,850,319 (Tangren) discloses a head suspension with a shorter spring region and a stiffener formed in the top profile of the load beam. The stiffener covers the proximal portion of the rigid region for increasing lateral and torsional stiffness. The stiffener decreases in width extending toward the distal end of the load beam.
Torsional modes, however, typically occur at lower frequencies, but typically have less of a lateral effect. Torsional modes are further subdivided depending on the number, if any, of nodes present along the length of the suspension assembly between a fixed end thereof and its free end. The slider would be supported near the free end. These various torsional mode shapes occur at different resonance frequencies. A single twist of the head suspension between a fixed end and its free end is referred to as first torsion mode. The off-track motion at the first torsion resonance frequency is the first torsional gain. Second torsional mode means a torsional mode shape having a single node along the length suspension between its fixed end and its free end. The position of the node divides the head suspension into first and second twisting motions on either side of the node point. Second torsional resonance frequencies occur at higher frequencies than the first torsional mode. Higher order torsional modes, i.e., third torsional mode having two node points, etc. typically occur at frequencies higher than those experienced within a typical disk drive environment.
The mass of the head suspension and how that mass is distributed along the head suspension has a large impact on the head suspension resonance frequencies, gain characteristics, and shock performance. For example, the addition of mass at a location of maximum displacement for a particular mode (bending or torsional) will generally reduce the natural frequency. Moreover, the lowering of the natural frequency may also increase the gain and shock performance. Mass located closer to the spring region is less detrimental to shock performance than mass loser to the distal end. To complicate matters, mass added at a specific location may advantageously increase lateral stiffness and thus the lateral bending mode resonance frequency, for example, but at the same time have a negative effect on a torsional resonance frequency.
To provide a high lateral bending frequency, the head suspension needs to be stiff in both the lateral direction and torsionally along the entire length of the head suspension. If a head suspension is designed with only one of these conditions in mind, the head suspension may have a low resonance frequency of torsional or lateral bending with a high degree of off-track motion or gain. A head suspension having a high lateral stiffness but a low torsional stiffness will not move strictly laterally due to the high lateral stiffness, but may twist at a lower resonance frequency. If the head suspension has high torsional stiffness and low lateral stiffness, the head suspension may deflect primarily laterally at a lower resonance frequency.
As an example, a wide head suspension load beam is described in U.S. Pat. No. 4,992,898 to Wanlass. The relatively wide and evenly spaced side edges of the Wanlass design provide a load beam having a relatively high lateral stiffness. However, this increase is at the expense of torsional stiffness, which without further compensating features would tend to reduce the resonance frequency of the torsional and sway modes.
An example of a head suspension load beam shape designed primarily to increase torsional resonance frequencies is shown in U.S. Pat. No. 5,027,240 to Zarouri, et al. In this case, mass is reduced significantly along the length of the head suspension to increase its torsional stiffness. However, this decrease in mass along the head suspension length has a negative effect in lateral stiffness. Again, while one stiffness is increased, the other is reduced.
The present invention is directed to a head suspension assembly for a rigid disk drive. The load beam has a mounting region at a proximal end, a rigid region at a distal end and a spring region connecting the mounting region and the rigid region. A pair of rails extend along a portion of the rigid region. The rigid region has a railed region and a non-railed region adjacent to the spring region. A stiffener is attached to the load beam in a multi-layered structure. The stiffener has a proximal portion extending along at least a portion of the non-railed region without extending into the spring region, and a distal portion extending along 50% or less of a length of the railed region closest to the spring region.
In one embodiment, the railed region and/or the non-railed region have a delta shape. The load beam preferably comprises a metal having a thickness of 0.0025 inches or less.
In one embodiment, the proximal portion of the stiffener has a delta shape. In another embodiment, the stiffener has a shape generally corresponding to a shape of the non-railed region. The stiffener can be any regular or irregular shape, such as rectangular or curvilinear. In another embodiment, the distal portion of the stiffener has a shape generally corresponding to a shape of the railed region of the rigid region closest to the spring region.
In one embodiment, the distal portion of the stiffener is attached to less than 40% of the length of the railed region closest to the spring region. In another embodiment, the distal portion of the stiffener is attached to about 20% of the length of the railed region closest to the spring region. The stiffener preferably comprises a thin metal having a thickness of about 0.002 inches to about 0.004 inches. The stiffener is typically attached to the load beam by welds, although adhesives can be used. In one embodiment, the welds are located at each corner of the stiffener.